Special variables

Special variables allow access to information about the size and georeferencing information of channels being operated on, as well as the position of the current pixel.

The following special variables may be treated as elements in modeling expressions:

@x: current x (pixel) processing location
@y: current y (line ) processing location
@dbx: size of database in x (pixel) direction
@dby: size of database in y (line ) direction
@meterx: size of a pixel in x direction in meters
@metery: size of a pixel in y direction in meters
@geox: x georeferenced center of current pixel
@geoy: y georeferenced center of current pixel
@sizex: x size of a pixel in georeferenced units
@sizey: y size of a pixel in georeferenced units

Note that @x, @y, @geox and @geoy change value for each pixel processed, while @dbx, @dby, @meterx, @metery, @sizex and @sizey remain constant over the whole image.

It is usually necessary to use the @x and @y special variables when constructing subscript expressions for channel expressions. For example, the following assignment would mirror an image across a vertical center line. The @dbx is used in computing the center line.

  %2 = %1[@dbx-@x+1,@y]